The fastest Crucial V4 SSD Sata II, with a capacity of 256 GB to 230 MB / s read and 190MB / s write, against 500 MB / s and 260 Mb / s for the M4. If the performance of the Crucial SSD seems modest, they remain well above those of a 2.5-inch hard drive, including the best models offer speeds of around 110 MB / s. Thus, you double your reading speed.